Axial flow pump

ABSTRACT

Disclosed is an axial flow pump including a combined impeller integrally formed of an axial impeller and a centrifugal impeller, the axial impeller being composed of a first cylinder on which a first groove is formed, the centrifugal impeller being composed of a second cylinder on which a second groove is formed. The second groove is smoothly connected with the first groove and a distance between a bottom surface of the second groove and a centerline of the second cylinder gradually increases to prevent turbulent flow of liquid which may occur at the connection point between first and second grooves thereby achieving a high pump performance and a decreased external size of the pump.

CROSS REFERENCE OF THE INVENTION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-321469 filed on Nov. 5, 2004, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pump for transporting liquid and more particularly to an axial flow pump having a combined impeller including an axial impeller and centrifugal impeller.

2. Description of the Related Art

Conventionally, a pump including an impeller is employed to transport liquid. As an example of the pump, Japanese patent application Kokai publication No. 2000-262404 discloses an axial flow pump in which an impeller formed to seemingly combine an axial impeller with a centrifugal impeller is provided. In the pump including the axial and centrifugal impellers, rotation of the axial impeller causes liquid taken from an inlet port to move in a direction along with a centerline of the axial impeller and rotation of the centrifugal impeller subsequently causes the liquid to discharge from an outlet port in a centrifugal direction substantially perpendicular to the centerline of the axial impeller.

When the liquid transported by the axial impeller reaches the centrifugal impeller, a traveling direction of the liquid suddenly changes from the direction along with the centerline of the axial impeller to the centrifugal direction. Due to this rapid change, a turbulent flow of the liquid occurs. This turbulent flow of the liquid causes deterioration in the liquid discharge performance by the pump.

To prevent the turbulent flow phenomenon, a rectifier plate may be is needed to be set where the turbulent flow occurs. However, such installation of the rectifier plate may also cause complexity in the entire structure of the impeller and increase in the external size of the pump, as well.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to prevent a turbulent flow of liquid in an axial flow pump.

It is another object of the invention to provide a unique structure of a combined impeller including an axial impeller and a centrifugal impeller in an axial flow pump.

To accomplish the above-described objects, an axial flow pump comprises a housing having a cylindrical wall defining a liquid passage inside the housing, the housing having opposite sides; an inlet port, formed at one side of the housing, which is fluidly communicated with the passage; an outlet port, formed at the other side of the housing, which is fluidly communicated the passage; and a combined impeller rotatably arranged along a center line of the cylindrical wall to forcibly generate flow of the liquid through the inlet port and discharge the liquid out of the outlet port, the combined impeller including an axial impeller and a centrifugal impeller which are located, in order, along the passage from the inlet port to the outlet port, the axial impeller being composed of a first cylinder having a first outer diameter and a first groove spirally formed on the first cylinder, and the centrifugal impeller being composed of a second cylinder having a second outer diameter larger than the first outer diameter and a second groove spirally formed on the second cylinder, wherein the second groove is smoothly connected with the first groove through a connection point and the second groove is shaped such that a distance between a bottom surface of the second groove and a rotational center of the centrifugal impeller gradually increases from the connection point in a direction opposite to the rotational direction of the combined impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of a pump in a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit for driving the pump.

FIG. 3 is a perspective view with a part of longitudinal cross section of a combined impeller employed in a pump of the first embodiment.

FIG. 4 is a perspective view of the combined impeller of the first embodiment.

FIG. 5 is a plan view of the combined impeller of the first embodiment.

FIG. 6 is a perspective view of a combined impeller employed in a second embodiment of the present invention.

FIG. 7 is a plan view of the combined impeller of the second embodiment.

FIG. 8 is a graph showing a relation among area ratio of a forcing surface to an entire surface of a second groove, pump performance of discharging air taken in liquid, and degree of a load affecting the pump.

FIG. 9 is a perspective view of the combined impeller of a third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. However, the same numerals are applied to the similar elements in the drawings, and therefore, the detailed descriptions thereof are not repeated.

A first embodiment of the present invention will now be described with reference to FIGS. 1 through 5.

FIG. 1 is a longitudinal cross sectional view of an axial flow pump 1 which transports liquid. The pump 1 includes a housing 3 having a cylindrical can 12 that has opposite sides and defines a liquid passage 2 therein. The pump 1 also has a combined impeller 4 rotatably arranged along a centerline of the cylindrical can 12. An inlet port 5 at one side of the housing 3 and an outlet port 6 at the other side of the housing 3 are respectively formed to fluidly communicate with the liquid passage 2. Rotation of the combined impeller 4 forcibly generates flow of the liquid along the liquid passage 2 through the inlet port 5 and discharges the liquid out of the outlet port 6.

To rotate the combined impeller 4,around the centerline, a stator 7 is arranged in the housing 3 to be opposite to the combined impeller 4 through the cylindrical can 12. The stator 7 is formed of a stator core 8, a plurality of windings 9, and bobbins 10. The stator core 8 is formed by laminating a plurality of silicon steel plates each shaped in a circular disk such that six projections 8 a protruding toward a centerline of the cylindrical can 12 are radially allocated by 60 degrees. The six windings 9 are set on the respective projections 8 a, separating three pairs each serially connected. One of the pairs of the windings 9 is aligned on two projections opposite to each other. The three pairs of the windings 9 are sequentially energized by supplying a driving current to magnetize the respective projections 8 a.

As shown in FIG. 2, the driving current is sequentially supplied from a driving unit 30 to the pairs of windings 9 so that the combined impeller 4 rotates by an associated operation between magnetization of the respective projections 8 a in sequence and permanent magnet provided in the combined impeller as described below. The bobbin 10 provided between the winding 9 and the projection 8 a is made of an insulating material to insulate both of them.

Between the bobbin 10 and projection 8 a a clearance is formed, and silicon grease 11 having a viscosity and thermal conductivity is introduced into the clearance. The silicon grease 11 is a gelled oil based material containing alumina powder having a high thermal conductivity to fill the clearance.

The cylindrical can 12 defining the liquid passage 2 in the housing 3 keeps the liquid away from contacting with the stator 7. In addition to the waterproof of the stator 7, since the cylindrical can 12 is made of highly thermal conductive material, such as metal, heat generated by the stator 7 travels through the cylindrical can 12 to the liquid passing through the liquid passage 2 thereby cooling the stator 7.

In the cylindrical can 12, a part of the combined impeller is arranged as described later. The combined impeller 4 has a shaft 16 which is rotatably supported by two ball bearings 17 and 18 attached respectively to the inlet port 5 side and the outlet port 6 side of the housing 3.

The combined impeller 4 is to be integrally formed, as a one piece, of an axial impeller 13 and a centrifugal impeller 14. The axial impeller 13 is located inside the cylindrical can 12 at one side of the housing 3 where the inlet port 6 is arranged. The centrifugal impeller 14 is located at the other side of the housing 3 where the outlet port 6 is arranged. When the combined impeller 4 rotates by the magnetization of the projections 8 a, the liquid drawing via the inlet port 5 travels through the axial and centrifugal impellers 13 and 14 in order.

The axial impeller is composed of a first cylinder 13 a having a first outer diameter slightly smaller than an inner diameter of the cylindrical can 12 and a first groove 13 b spirally formed on a periphery of the first cylinder 13 a. The centrifugal impeller 14 is composed of a second cylinder 14 a having a second outer diameter larger than the first outer diameter and a second groove 14 b spirally formed on a periphery of the second cylinder 14 a. The first groove 13 b and the second groove 14 b are smoothly connected as described later.

In general, it may be understood that a groove is defined by opposite walls and a bottom surface between walls. In this embodiment, however, as shown in FIGS. 4 and 5, one of the walls of the groove is eliminated to simplify the structure and the bottom wall of the housing 3 facing the centrifugal impeller 14 acts as the other wall of the groove in view of the operation of the pump. Therefore, in this embodiment, such modified groove having one wall and a bottom surface is also called as a groove.

In FIG. 3 the combined impeller 4 is manufactured by molding polyphenylene sulfide to integrally form the axial and centrifugal impellers 13 and 14. The axial impeller 13 includes two rotor cores 26 and a permanent magnet 25 which locates between the cores to generate magnetic poles on the rotor cores. When molding, two rotor cores 26 are positioned into the axial impeller 13 such that the magnetic poles of the rotor cores 26 face, via the cylindrical can 12, to the projections 8 a provided with the windings 9 when the pump is assembled. The rotor cores 26 are radially allocated about a centerline of the combined impeller 4 such that different magnetic poles are alternately placed by 90 degrees.

As shown in FIG. 4, the first groove 13 b on the axial impeller 13 is shaped such that a distance between a bottom surface 13 c of the first groove 13 b and a rotational center of the axial impeller 13 is uniformed over the entire region of the first groove 13 b. The first groove 13 b is also spirally shaped at an angle ranging from 12 to 25 degrees with respect to the centerline of the axial impeller 13.

The second groove 14 b on the centrifugal impeller 14 is smoothly connected with the first groove 13 b through a connection point A as indicated in FIG. 4. The second groove 14 b is spirally and extendedly shaped such that a distance between a bottom surface 14 c of the second groove 14 b and a rotational center of the centrifugal impeller 14 gradually increases from the connection point A in a direction opposite to the rotational direction of the combined impeller 4. At the connection point A between the first groove 13 b and the second groove 14 b, the bottom surface 13 c of the first groove 13 b is smoothly connected with the bottom surface 14 c of the second groove 14 b. Because the second groove 14 b is spirally and extendedly formed on the second cylinder 14 a as stated above, a termination edge 14 d emerges at a position that the second groove 14 b terminates on the second cylinder 14 a. Besides, owing to the spirally formed groove, a width B, B′ of the bottom surface 14 c of the second groove 14 b in a direction along the center line of the combined impeller 4 gradually decreases toward the bottom surface termination edge 14 d.

In the pump 1 described above, the combined impeller 4 can be driven in a rotational direction as indicated by an arrow C in FIGS. 4 and 5 by means of the driving unit 30 that supplies a driving current to the respective pairs of windings 9 to sequentially change the magnetic poles of the respective projections 8 a in the stator 7.

By the rotation of the combined impeller 4, liquid is taken through the inlet port 5, carried through the first groove 13 a on the axial impeller 13 and then transferred from the first groove 13 a to the second groove 14 b via the connection point A without generating a turbulent flow of the liquid at the connection point A. This is because that a flow direction of the liquid is gradually and smoothly changed at the connection point A toward a centrifugal direction indicated by an arrow D by the bottom surface 14 c of the second groove 14 b as the combined impeller 4 (centrifugal impeller) rotates. After that, the flow direction of the liquid is further changed from the centrifugal direction to the rotational direction of the combined impeller 4 as the centrifugal impeller further rotates because of the absence of side wall extending from the can 12 and then the liquid is discharged from the outlet port 6.

In respect to a method of manufacturing the combined impeller 4 in this embodiment, a molding method is employed to integrally form the axial and centrifugal impellers 13 and 14 at the same time without unevenness at the connection point A between the first and second grooves 13 b and 14 b. Alternatively, after the axial and centrifugal impellers are separately formed, manufacturing method may be employed in which the axial and centrifugal impellers are bonded to each other to smoothly connect the first groove on the axial impeller with the second groove on the centrifugal impeller.

The pump including the aforementioned combined impeller achieves a smooth liquid transfer without occurrence of turbulent flow at the connection point A from the axial impeller to the centrifugal impeller. Due to a unique structure of the combined impeller, applying a rectifier plate between an axial and centrifugal impellers is not needed to achieve a smooth liquid transfer. Therefore, performance of the pump can be improved without the rectifier plate.

As the rectifier plate and room for setting the rectifier plate are not needed, the external size of the pump can be decreased compared with a pump which employs such rectifier plate.

Besides, as indicated by B and B′ in FIG.4, since a width of the bottom surface 14 c of the second groove 14 b in a direction along the center line of the cylindrical wall gradually decreases toward a direction opposite to the rotational direction of the combined impeller, load adversely affecting the rotation of the combined impeller 4 which otherwise increases as the combined impeller 4 rotates can be alleviated.

A second embodiment of the present invention is described with reference to FIGS. 6 through 8. FIG. 6 is a perspective view of a modified combined impeller 20 employed in an axial flow pump of this embodiment. FIG. 7 is a plan view of the combined impeller 20.

A combined impeller 20 of the second embodiment is housed in the housing 3 shown in FIG. 1, instead of the combined impeller 4. A difference between the first embodiment and the second embodiment is a structure of the combined impeller. In particular, a major difference between the combined impeller 4 of the first embodiment and the combined impeller 20 of the second embodiment is a structure of the centrifugal impeller 14A. Therefore, description will be given only to the structure of the combined impeller 20.

The combined impeller 20 is integrally formed, as one piece, of an axial impeller 13 and a centrifugal impeller 14A. The axial and centrifugal impellers 13 and 14A are placed such that liquid taken from the inlet port 5 firstly goes through the axial impeller 13, and then goes through the centrifugal impeller 14A, as shown in FIG. 1.

The axial impeller 13 is composed of a first cylinder 13 a having a first outer diameter slightly smaller than an inner diameter of the cylindrical can 12 and a first groove 13 b spirally formed on a periphery of the first cylinder 13 a.

The centrifugal impeller 14A is composed of a second cylinder 14 a having a second outer diameter larger than the first outer diameter and a second groove 14 b spirally and extendedly formed on a periphery of the second cylinder 14 a. The second groove 14 b is smoothly connected with the first groove 13 b at a connection point A, as shown in FIG. 6. Thus, the combined impeller 20 in this embodiment has two continuous grooves comprised of the first and second grooves.

Since the second groove 14 b is spirally and extendedly formed on the second cylinder 14 b, a bottom surface 14 c of the second groove 14 b has a termination edge on the second cylinder 14 a. At the termination edge, the bottom surface 14 c projects toward a rotational direction of the combined impeller 20 to form a forcing surface 21. In more detail, the bottom surface 14 c is shaped such that a part of the bottom surface 14 c near the termination edge smoothly curves toward the rotational direction of the combined impeller 20. By such a construction of the second groove 14 b, liquid which is conveyed along the second groove 14 b as the combined impeller 20 rotates is finally forced to change its flow direction by the forcing surface 21 along with substantially a tangential direction of the second cylinder 14 a. A projecting area G of the forcing surface 21 may be formed to be 30% or less to the entire area F of the bottom surface 14 c from the connection point A to the termination edge as shown in FIG.7.

An operation of the forcing surface 21 will be described in more detail. Rotation of the combined impeller 20 causes conveyance of liquid from the inlet port 5 to the outlet port 6 through the combined impeller 20, as shown in FIG. 1. When forwarding the liquid from the centrifugal impeller 14A of the combined impeller 20 to the outlet port 6, the liquid is forwarded by the bottom surface 14 c toward the direction indicated by the arrow D and then is forced to flow by the forcing surface 21 toward the tangential direction of the second cylinder 14 a indicated by an arrow E, i.e., the rotational direction of the combined impeller 20, as the rotation of the combined impeller 20 advances. The flow direction of the liquid is thus changed to the rotational direction of the combined impeller 20 by the forcing surface 21 and the liquid is finally discharged from the outlet port 6.

In general, pumps may draw liquid with air bubbles into the inside thereof or air bubbles may be produced during transfer of liquid within a pump. Such air bubbles may stay in the pump and adversely affect performance of the pump. However, in this embodiment, since the forcing surface 21 forcibly and smoothly changes the flow direction of liquid from the axial direction to the rotational direction of the combined impeller 20, air bubbles are also forwarded together with the liquid to the outlet port 6 and are finally discharged out of the port 6. Therefore, performance of the pump can be improved by the forcing surface.

FIG. 8 is a graph showing pump performance of discharging air bubbles contained in liquid and degree of load affecting the combined impeller 20 respectively in terms of each ratio in an area of the forcing surface 21 to an entire area of the bottom surface 14 c when the ratio is varied. As can be seen, the larger the area ratio goes, the higher the pump performance becomes. However the degree of the load adversely increases in accordance with the area ratio. Thus, it is preferred to set the area ratio to be 30% or less.

A third embodiment of the present invention is described with reference to FIG. 9. In the above-described first and second embodiments, the centrifugal impeller 14 (14A) includes the second cylinder 14 a on the outer surface of which the second groove 14 b having one wall and a bottom surface is formed. The third embodiment includes a further modified combined impeller 30.

General structure of a pump in this embodiment is like the pump described in the first embodiment. The further modified combined impeller 30 is formed such that a circular top plate 14 e is set on the second cylinder 14 a of the combined impeller 4 shown in FIG. 1. The circular top plate 14 e has a diameter equal to or slightly larger than the outer diameter of the second cylinder 14 a.

When manufacturing the combined impeller 30, it is possible to fix the circular top plate 14 e with the second cylinder 14 a or to integrally mold the combined impeller 30 including an axial and centrifugal impellers 13, 14 and the circular top plate 14 e.

The above-described combined impeller 30 is driven by the driving unit 9 as similar to the first embodiment. When the combined impeller 30 rotates in the pump, liquid transferred from the first groove 13 b is forwarded toward a radial direction of the combined impeller 30 by the bottom surface 14 c. Then the circular top plate 14 e functions to assist the centrifugal impeller 14 to forcibly move the liquid, which otherwise flows in the axial direction, toward the radial direction thereof. Therefore, the circular top plate 14 e of the centrifugal impeller 14 can improve performance of the pump.

Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the present invention can be practiced in a manner other than as specifically described therein. 

1. A pump for transporting liquid, comprising: a housing having a cylindrical wall defining a liquid passage inside the housing, the housing having opposite sides; an inlet port, formed at one side of the housing, which is fluidly communicated with the passage; an outlet port, formed at the other side of the housing, which is fluidly communicated the passage; and a combined impeller rotatably arranged along a center line of the cylindrical wall to forcibly generate flow of the liquid through the inlet port and discharge the liquid out of the outlet port, the combined impeller including an axial impeller and a centrifugal impeller which are located, in order, along the passage from the inlet port to the outlet port, the axial impeller being composed of a first cylinder having a first outer diameter and a first groove spirally formed on the first cylinder, and the centrifugal impeller being composed of a second cylinder having a second outer diameter larger than the first outer diameter and a second groove spirally formed on the second cylinder, wherein the second groove is smoothly connected with the first groove through a connection point and the second groove is shaped such that a distance between a bottom surface of the second groove and a rotational center of the centrifugal impeller gradually increases from the connection point in a direction opposite to the rotational direction of the combined impeller.
 2. A pump according to claim 1, wherein the second groove has a bottom surface termination edge and includes a forcing surface, formed on the bottom surface termination edge, which projects toward the rotational direction of the combined impeller to push out the liquid along with substantially a tangential direction of the second cylinder.
 3. A pump according to claim 2, wherein the projecting area of the forcing surface is 30% or less to the entire area of the bottom surface of the second groove from the connection point to the bottom surface termination edge.
 4. A pump according to claim 2, wherein the bottom surface of the second groove is formed such that a width of the bottom surface in a direction along the center line of the cylindrical wall gradually decreases toward the bottom surface termination edge.
 5. A pump according to claim 1, wherein the second groove has a bottom surface termination edge and the bottom surface of the second groove is formed such that a width of the bottom surface in a direction along the center line of the cylindrical wall gradually decreases toward the bottom surface termination edge.
 6. A pump according to claim 5, further comprising a circular top plate having a diameter equal to or larger than the second diameter and provided on a surface having the bottom surface termination edge.
 7. A pump according to claim 1, further including a driving unit for supplying a driving current to drive the combined impeller and a stator having windings, the stator being opposite to the combined impeller through the cylindrical wall in the housing.
 8. A pump according to claim 7, wherein the combined impeller includes a plurality of magnets arranged at a distance along the rotational direction inside the combined impeller, and the combined impeller is rotated around the rotational center when the driving unit supplies a driving current to the windings of the stator. 